Method for Connecting a Component With a Substrate

ABSTRACT

An apparatus for connecting a component with a substrate by means of diffusion soldering in a closed evacuated chamber, wherein the component and the substrate to be connected are displaceable separate from one another in the chamber, and the chamber comprises a combined transfer and pressing unit being displaceable between a current position of the component and a current position of the substrate, for placing and pressing the component on the substrate, and the combined transfer and pressing unit comprises a rotatable element, which, in response to the placing and pressing of the component on the substrate, assumes an angle between the normal of a lower side of the component to be connected and a pressing direction of the component, the angle corresponding to an angle between the normal of a surface area of the substrate to be connected and the pressing direction of the component.

PRIORITY CLAIM

This application is a divisional of, and claims priority to, U.S.application Ser. No. 11/688,039 filed 19 Mar. 2007, the content of whichapplication is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method for connectinga component to a substrate by means of diffusion soldering in a chamber.

BACKGROUND

Electronic modules comprise power electronic circuits, such as invertersand rectifiers, for example. Often, a plurality of substrates isarranged on a metal base plate and integrated into a module.Metallization layers are likewise deposited on the front side (e.g. astructured layer) and the rear side of the substrates so as to connectsemiconductor devices and components to the front side and the metallicbase plate to the rear side of the substrate by means of soft-solderingvia solder layers.

In a soft-soldering process, a solder paste is applied to the substratesby means of template printing or ink jet methods. Subsequently, thedevices are placed on the solder paste surfaces. The fitted substratesare automatically transported in a soldering furnace (vacuum continuousfurnace, batch furnace, vapor-phase oven, etc.). There, heat isintroduced into the substrates and the solder is remelted.

Diffusion soldering provides an alternative technology tosoft-soldering. During diffusion soldering, a common soft solder isused, whereby, contrary to the paste-soldering, the target layerthickness is reduced. A common heating channel may be used for diffusionsoldering of semiconductor devices, which are inserted into the heatingchannel through an opening. The devices are soldered in an open heatingchannel such that a flowing forming and protective gas atmosphere and acontact pressure are present for a period of time. The heating channelis divided into three sections. For a homogeneous flow of the protectivegas and for minimizing a contamination of the protective gas flowthrough the opening the surface of the opening is rather small so thatthe discharge of the protective gas only slightly disrupts thehomogeneous flow of the protective gas.

The open heating channels do not provide an opportunity to useaggressive media as an activating atmosphere for the reduction ofoxidized surfaces of the devices. Thus, there is a need to providechannels allowing the use of aggressive media.

SUMMARY

An apparatus for connecting a component with a substrate by means ofdiffusion soldering in a closed evacuated chamber, where the componentand the substrate to be connected are displaceable separate from oneanother in the chamber, and the chamber comprises a combined transferand pressing unit being displaceable between a current position of thecomponent and a current position of the substrate, for placing andpressing the component on the substrate, and the combined transfer andpressing unit comprises a rotatable element, which, in response to theplacing and pressing of the component on the substrate, assumes an anglebetween the normal of a lower side of the component to be connected anda pressing direction of the component, the angle corresponding to anangle between the normal of a surface area of the substrate to beconnected and the pressing direction of the component.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel connection arrangement can be better understood with referenceto the following drawings and description. The components in the figuresare not necessarily to scale, instead emphasis is placed uponillustrating the principles of the novel arrangement. Moreover, in thefigures, like reference numerals designate corresponding parts. In thedrawings:

FIG. 1 is a cross sectional view of a power semiconductor module withelectronic components on two substrates and a base plate;

FIG. 2 is a schematic view of a common open heating channel with threesections;

FIG. 3 is a schematic view of a common open heating channel withenlarged opening compared to FIG. 2A;

FIG. 4 is a top view of an example of a novel apparatus for diffusionsoldering with three subchambers;

FIG. 5 is a cross sectional view of a novel chamber for diffusionsoldering in another example with a transfer and pressing unit havingplunges, which are elastically connected to one another;

FIG. 6 is a cross sectional view of a transfer and pressing unit withplunges, which prevent tiltings between components and substrates via ashared rotatable element;

FIG. 7 is a cross sectional view of a transfer and pressing unit inanother example, whereby each plunge comprises an individual rotatableelement;

FIG. 8 is a cross sectional view of a transfer and pressing unit in yetanother example, whereby the plunges are connected to one another overan elastic cell comprising a liquid and of a membrane, which seals theliquid;

FIG. 9 is a cross sectional view of a transfer and pressing unit in anexample, whereby each plunge is connected to the plunge carrier in anindividually movable and spring-mounted manner;

FIG. 10 is a cross sectional view of one of the plunges of FIG. 7,whereby the rotatable element comprises a cardanic element;

FIG. 11 is a cross sectional view of another of the plunges of FIG. 7,whereby the rotatable element comprises two cardanic elements beingconnected in series;

FIG. 12 is a cross section view of a cardanic element with a sphere, anupper part, and a lower part;

FIG. 13 is a schematic view of the lower part of FIG. 12; and

FIG. 14 is a schematic view of the upper part of FIG. 12.

DETAILED DESCRIPTION

In the common power electronic module 15 of FIG. 1, the semiconductordevices 5, 6, 7, 8, are integrated on substrates 1, 2, whereby thedevices 5, 6 are arranged on the substrate 1, and the devices 7, 8 arearranged on the substrate 2. The substrates 1, 2 are non conductiveceramics for voltage isolation, such as Al₂O₃, doped Al₂O₃, AlN orSi₃N₄, for example. For assembling and contacting the semiconductordevices 5, 6, 7, 8 on the substrates 1, 2, at least the upper sides ofthe ceramic substrates 1, 2 are metallized with Cu, Ni, Al or a similarmaterial (metal layer 11). The metal layer 11 is connected with theceramic substrate 1, 2 by means of a DCB (direct copper bonding) or anAMB (active metal brazing) process. A regular brazing type substrate maybe used alternatively. In these kinds of metallization processes, metallayers with a roughness of about Rz=2-10 μm are created. The metal layer11 may be divided into separate strip conductors by performing anadditional etching process step for structuring of the layout of adesired circuit. Typically, layer thicknesses of the ceramic substrates1, 2 range from 0.2 to 2.0 mm. Typical thicknesses of the metallizationlayers 11 range from 0.1 to 0.6 mm.

Often, a plurality of substrates 1, 2 is integrated in the module 15 ona metal base plate 9. In this case, a metallization 10 is likewiselocated on the rear side of the substrates 1, 2, for the production of aconnection to the metallic base plate 9 by means of soft-soldering viathe solder layers 12. A high thermal conductivity and a heatcoefficient, which should be adapted to that of the substrates 1, 2, aredesirable for the base plate 9. Cu and the composite material AlSiC aresuitable materials for the base plate 9.

A housing 14 comprising a technical plastic is either glued to the baseplate 9 or the substrates 1, 2. The housing 14 protects the electriccomponents against outside meteorological influences and comprisessilicon gel 16, with which the module 15 is typically cast. The silicongel 16 ensures electric isolation within the module 15.

The semiconductor devices 5, 6, 7, 8 are connected to the metallizationlayers 11 on the substrates 1, 2, by soft-soldering with alloys such asSn—Pb, Sn—Ag, Sn—Ag—Cu or other lead-free solder materials via solderlayers 13. The connection of the metallic base plate 9 to themetallization layers 10 on the lower side of the substrates 1, 2 is alsomade—as mentioned above—by soft-soldering through the layers 12.

The low melting point of the solder alloys in the layers 12, 13 of 183°C. for SnPb₄₀ and 221° C. for SnAg_(3.5), for example, eliminates a useunder operating temperatures Tc of the devices 5, 6, 7, 8 at 175° C. Atthis temperature, the solder is operated too closely to its meltingpoint, so that a sufficient thermal long-term stability cannot beguaranteed. In this case, the solder 13 is subjected to high stresses,caused by the changing thermal loads arising at the location of thedevices 5, 6, 7, 8 during operation of the module 15. After a shortperiod of time, cracks may form in the solder 13 leading to a breakdownof the devices 5, 6, 7, 8 caused by overheating.

The semiconductor devices 5, 6, 7, 8 are connected to the substrates 1,2 by soft-soldering. At first, a solder paste 13 is applied to thesubstrate 1, 2 by template printing, ink jet methods or the like.Subsequently, the devices 5, 6, 7, 8 are automatically placed onto thesolder past surfaces 13. Furthermore, the fitted substrates 1, 2 areautomatically transported in a soldering furnace (vacuum continuousfurnace, batch furnace, vapor-phase oven, etc.). There, heat isintroduced into the substrates 1, 2 and the solder 13 is remelted. Areliable electrically and thermally stable connection is formed throughthe formation of an alloy at the boundary surfaces between the devices5, 6, 7, 8 and the substrates 1, 2.

At operating temperatures of the devices 5, 6, 7, 8 of Tc=175° C. andabove, the diffusion soldering provides an alternative technology.During diffusion soldering, a common soft solder is used. However,contrary to the paste-soldering, the target layer thickness is reducedfrom approximately 100 μm to several μm. With a sufficiently longsoldering period, the entire solder is transferred into a high-meltingintermetallic phase by means of alloy formation. Due to the fact thatresidual solder does not remain, a connection and contact layer havingmelting temperatures far above 200° C. is created.

FIG. 2 illustrates a common heating channel 20 for diffusion solderingof semiconductor components, which are inserted into the heating channel20 through the opening 21 at the upper side of the heating channel 20.The (non-illustrated) components are soldered in the open heatingchannel 20 under a flowing forming and protective gas atmosphere 29 fora period of time t under a contact pressure F, so that a completetransfer of the solder is realized in a high-melting intermetallicphase. The heating channel 20, which is divided into three sections 22,23, 24, leads to diffusion-soldered layers with thicknesses of between 1and 20 μm. For a homogeneous flow of the protective gas 29 and for aminimization of the contamination of the protective gas flow 29 throughthe opening 21 into the heating channel 20, it is necessary to choosethe surface of the opening 21 to be so small that the discharge 27 ofthe protective gas 29 only slightly disrupts the homogeneous flow of theprotective gas 29.

Compared to the surface of the opening 21 of the heating channel 20 ofFIG. 2, the heating channel 25 of FIG. 3 has an opening 26 with anenlarged surface. The opening 26 is suitable for soldering surfaceslarger than 200 mm² and for a plurality of simultaneouslydiffusion-soldered components in the heating channel 25.

During diffusion-soldering of components with comparatively smallsoldering surfaces and correspondingly small openings 21, the channelcan be constructed by generating of a suitable course of the flow of aprotective gas 29 such that the oxygen contamination of the protectivegas 29 through the opening 21 is kept below 100 ppm. Compared to theheating channel 20, the oxygen concentration in the heating channel 25rises and assumes an increasingly undefined value. Furthermore, theprotective gas 28, which escapes through the opening 26, leads to anincreasingly inhomogeneous protective gas distribution within theheating channel 25, as compared with the heating channel 20. The resultis an increased rate of hollow spaces inside the generated solder layerduring diffusion-soldering, and a higher rate of dents at the surface ofthe solder layer.

Mechanical systems for diffusion-soldering of semiconductor componentswith solder surfaces of up to 200 mm² to metallized ceramic substrateswith a roughness of Rz=2-10 μm with open heating channels are known, inwhich the components are placed and pressed on a substrate in twotemporally and spatially separate steps. However, because the timebetween placing and pressing the component on the substrate is to bekept as short as possible during diffusion-soldering, a prematuremelting and an uncontrolled alloy formation of the solder can occur.

Furthermore, the open heating channels 20, 25 described in FIGS. 2 and 3do not provide an opportunity to use aggressive media as activatingatmosphere for the reduction of oxidized surfaces of the components. Asubsequent and controlled reduction of oxidized surfaces, however, isdesirable particularly during the processing of Cu surface areas havinga high purity grade.

A vacuum-continuous apparatus for simultaneous, automatic diffusionsoldering of a plurality of components on a plurality of substrates isillustrated in FIG. 4. In an example, the diffusion soldering plant 30comprises three subchambers 40, 50, 60, which are separated from

The devices 5, 6, 7, 8, which are to be connected, and the substrates 1,2, which are to be connected, are displaced inside the chamber 30 oncarrier systems 41, 42, which are separated from one another. One or aplurality of substrates 1, 2 are introduced on a first carrier system 41into the subchamber 40 via the lock 32 and are heated to a first processtemperature T1 via the heating plate 36 of the subchamber 40. One or aplurality of devices 5, 6, 7, 8 are located on a second carrier system42, which also introduces the devices 5, 6, 7, 8 into the subchamber 40of the diffusion chamber 30 by passing through the lock 32. The devices5, 6, 7, 8 are heated to the process temperature T2 via the heatingplate 37.

As shown, the direction of displacement of the devices 5, 6, 7, 8 and ofthe substrates 1, 2 is provided in a straight route through the chamber30 (arrows 29). The carrier systems 41, 42 run parallel to one anothercontinuously in longitudinal direction of the diffusion chamber 30 fromthe lock 32 to the lock 35.

Each subchamber 40, 50, 60 has a respective heating plate for thesubstrates and the devices. The substrates are thus heated to thetemperature T3 using the heating plate 52 in the subchamber 50 and thedevices are heated to the temperature T4 via the heating plate 51. Thetemperature T5 can be adjusted in the subchamber 60 via the heatingplate 38. In case of displacement directions of the carrier systems 41,42 opposite to one another, the temperature T6 of the devices 5, 6, 7, 8is adjustable on the heating plate 39.

On the side facing the carrier system 42, the devices 5, 6, 7, 8 have ametallization, which may be diffusion soldered, and which, as a solderlayer, establishes the connection to one or a plurality of substrates.Mechanical systems for evacuating the housing 31 of the diffusionsoldering chamber 30 and inlets for gas media individually for eachchamber 40, 50, 60 (not illustrated) provide for the desired atmosphereduring the diffusion soldering process. For activating the free surfaceareas of the components, aggressive, acid gas media, for example, areintroduced into the subchamber 50 prior to the soldering. Reducingmedia, such as formic acid, are used as activating media. Otheractivating media may be used as well.

A first gas exchange is affected in the subchamber 40, and a definedresidual oxygen concentration between 1 and 1000 ppm is adjusted. Afterthe end of the heating phase in the subchamber 40, which includes theheating of the substrates 1, 2 to the process temperature T1 and theheating of the devices 5, 6, 7, 8 to the process temperature T2, thesubstrates 1, 2 and the devices 5, 6, 7, 8 are displaced from thesubchamber 40 into the subchamber 50 via the lock 33. An activating gasmedium, for example formic acid, is introduced in the subchamber 50, toeliminate possible oxidic contaminations of the free surface areas ofthe devices 5, 6, 7, 8 and of the substrates 1, 2.

To minimize contaminations, which can permeate from the outside into thechamber 30 via the locks 32, 35, provision is made for a combinedtransfer and pressing unit 70 to be positioned in the center of thechamber 30.

Prior to the placing and pressing process of the devices 5, 6, 7, 8 onthe substrates 1, 2, the devices 5, 6, 7, 8, as well as the substrates1, 2 are displaced in positions, which permit a gripping of the devices5, 6, 7, 8 by the transfer and pressing unit 70 and a placing andpressing of the devices 5, 6, 7, 8 on the substrates 1, 2. In thefollowing, these positions are referred to as current positions. Thecombined transfer and pressing unit 70 is displaced between the currentposition of the devices 5, 6, 7, 8 and the current position of thesubstrates 1, 2. The combined transfer and pressing unit 70 grips thedevices 5, 6, 7, 8, which are to be connected, travels between thecurrent position of the devices 5, 6, 7, 8 and the current position ofthe substrates 1, 2, and deposits the devices 5, 6, 7, 8 on thesubstrates 1, 2. The transfer and pressing unit 70 thus simultaneouslyor consecutively removes the devices 5, 6, 7, 8 from the carrier system42 and simultaneously or consecutively places the devices 5, 6, 7, 8onto the positions of the substrates 1, 2 located on the first carriersystem 41, which are to be connected.

Immediately after the placement of the devices 5, 6, 7, 8 on the currentposition of the substrates 1, 2, the transfer and pressing unit 70homogeneously presses the devices 5, 6, 7, 8 on the substrate surfacearea with a defined pressure of between 0.1 to 5 N/mm². Naturally, it isalso possible to place and press a respective device 5, 6, 7, 8 to arespective substrate 1, 2 by means of the transfer and pressing unit 70.Because of the formic acid applied in the subchamber 50 to the surfaceareas of the devices 5, 6, 7, 8 and of the substrate 1, 2, which are tobe connected, the process temperature T3 in the subchamber 50 may bereduced.

After the transfer and pressing process, the fitted substrates 1, 2 aredisplaced into the subchamber 60 via the lock 34 to be cooled. For theclocking of further components, which are to be connected, the carriersystem 42 also travels from the subchamber 50 into the subchamber 60 viathe lock 34. In doing so, the heating phase, the transfer and pressingphase, as well as the cooling phase are effected in the subchambers 40,50, 60. The substrates 1, 2 fitted with the devices 5, 6, 7, 8 arecooled to room temperature in the subchamber 60 and are discharged viathe lock 35 from the diffusion soldering chamber 30 via the carriersystem 41.

In an another example, the chamber comprises a plurality of juxtaposedsubchambers 40, 50, 60, whereby each subchamber 40, 50, 60 comprises amedium and/or process temperature, which differs from that of the othersubchambers. Particularly a division of the chamber 30 into threesubchambers 40, 50, 60, as illustrated in FIG. 4, is advantageous,whereby a heating phase, a transfer and pressing phase, as well as acooling phase of the devices 5, 6, 7, 8 is effected on the substrates 1,2 in a respective subchamber 40, 50, 60. In response to a clockedcontinuous transport of the components, the heating phase, the transferand pressing phase, as well as the cooling phase may proceedsimultaneously to one another in the subchambers 40, 50, 60.

Optionally, the diffusion soldering chamber 30 with the threesubchambers 40, 50, 60, as depicted in of FIG. 4, may be expanded by oneor two chambers (not illustrated). A further chamber, in which thedevices 5, 6, 7, 8 undergo a temperature treatment at a later point maybe introduced behind the subchamber 50, for example. If the process inthe subchamber 40 is a process-time-limited step, a chamber mayfurthermore be introduced following the subchamber 40, which permits aprocess time adaptation to the processes taking place in the subchambers50 and 60.

In another example, the heating phase, the placing and pressing phase,and the cooling phase take place in only one chamber (not illustrated).

A diffusion soldering chamber 50 is illustrated in cross section in FIG.5. The transfer and pressing unit 70 is displaced between the currentposition of the devices 5, 6 and the substrates 3, 4 (see double arrow).The transfer and pressing unit comprises a plurality of plunges 53, 54,55, 56, which are each individually mounted in a movable andspring-mounted manner in the direction of the pressing direction of thedevices 5, 6 on the substrates 3, 4 (not illustrated). The plunges 53,54, 55, 56 are connected to one another via an elastic cell 58. A vacuumsuction element or similar equipment is integrated in each plunge 53,54, 55, 56 for receiving the devices 5, 6, so that the devices 5, 6located on the carrier system 42 are securely received by the plunges53, 54. In the embodiment illustrated in FIG. 5, the elastic cell 58comprises an elastomer and, in response to the placing and pressing ofthe devices 5, 6, leads to a homogeneous contact pressure F of between0.1 to 5 N/mm² on the upper side of the devices 5, 6, which is oppositeto the lower side of the devices 5, 6, which is to be connected.

The devices 5, 6 are lifted via the plunges 53, 54 and are moved via thetransfer and pressing unit 70, which is displaceable in the directionpredefined by the positioning rail 59, between the current position ofthe devices 5, 6 and the current position of the substrates 3, 4, whichpermit a reception of the devices 5, 6 and a deposition of the devices5, 6, on the substrates 3, 4, by means of the transfer and pressing unit70. Individual temperatures for the substrates 3, 4 and for the devices5, 6 are ensured by the heating plates 51, 52 below the carrier systems41, 42.

The plunges 53, 54, 55, 56 deposit the devices 5, 6 on the predefinedpositions on the substrates 3, 4 with sufficient accuracy, so that ashifting or rearrangement of the devices 5, 6, is not necessary afterthe devices 5, 6 have been placed on the substrates 3, 4. Alternativelyto a direction perpendicular to the direction of displacement of thecarrier systems 41, 42, the placing and pressing unit may be displacedin a plane, which is located parallel to the plane mounted by thesurface area of the carrier system 41. In this case, the position of adevice 5, 6, which is to be applied, can be variably aligned on thepositions on the substrates 3, 4 for the devices 5, 6.

FIG. 6 shows a further example of a placing and pressing unit 70 incross section. As illustrated in FIG. 5, the plunges 53, 54, 55, 56 aredisplaced in the direction of the contact pressure F and comprise vacuumsuction lines 73, 74, 75, 76, which discharge into vacuum suctionelements 9, 10. The vacuum suction lines 73, 74, 75, 76 discharge into asupply line 77, which is connected to a vacuum reservoir, for example avacuum pump (see Vak. in FIG. 6).

The plunges 53, 54, 55, 56 comprise a common rotatable element 72 forcompensating a tilting between the (non-illustrated) substrates and thecomponents to be connected. In response to a placing and pressingprocess of the components on the substrates, the rotatable element 72,which is located above or below the elastic cell 58 inside the tool basebody 71, for example, leads to an angle between the normal of the lowersides of the components, which are to be connected, and the pressingdirection of the components F. The angle corresponds to the anglebetween the normal of the substrate surface areas, which are to beconnected, and the pressing direction F of the components. The plane ofthe substrate surface areas is schematically illustrated in FIG. 6 bymeans of the carrier system 42.

A further example of a transfer and pressing unit 80 is illustrated inFIG. 7, whereby the plunges 87 each comprise individual rotatableelements 83, 84, 85, 86. The rotatable elements 82, 83, 84, 85, 86 mayeach comprise cardanic elements. As is the case in FIG. 6, the suctionlines of the plunges 87 herein are also connected to one another via thesupply line 77, which leads to a vacuum reservoir.

A variable force F, which is redirected into the devices 5, 6 via theplunges 53, 54, 55, 56, is injected by the transfer and pressing unit.The introduction of the force into the devices 5, 6 plays a central partfor the production of solder layers with thicknesses of a few μm. Carehas to be taken to completely alloy the solder layers in the shortestpossible time. To be able to compensate for differences in levelsbetween the different devices 5, 6, and to be able to inject the sameforces to all of the devices 5, 6, the transfer and pressing unitcomprises plunges, which are mounted in the tool base body 57 in amovably and spring-loaded manner in the direction of the pressing forceF.

A further exemplary arrangement of the haltering of the plunges 53, 54,55 in the tool base body 57 is illustrated in the transfer and pressingunit 90 of FIG. 8. Instead of the elastic cell 58, which comprises anelastomer, the guided plunges 53, 54, 55, are connected to one anothervia a liquid 91 and via a flexible membrane 92, which seals the liquid.

Another variant of the flexible storing of the plunges 53, 54, 55 in thetool base body 102 of the transfer and pressing unit 100 is illustratedin FIG. 9. The plunges 53, 54, 55 are individually connected to the toolbase body 102 via spring elements 101. Naturally, elastic cells, whichindividually connect the plunges 53, 54, 55 to the tool base body 102,may also be used instead of the spring elements 101. Possibledifferences in the levels between the devices 5, 6 are compensated forby compression of the spring-mounting of the plunges 53, 54, 55 and theforce F is evenly introduced into the devices 5, 6 and the substrates 3,4 via the plunges 53, 54, 55. The substrates 3, 4 are thereby maintainedon the process temperature T3 until the entire soft solder is alloyedand is located exclusively in the metallic phases in the solderconnection layer.

Different variants of the rotatable elements 82, 83, 84, 85, 86 areillustrated in FIGS. 10 and 11. The plunges schematically illustrated inFIGS. 10 and 11 each comprise suction lines 77. The plunge 87 onlycomprises one cardanic element 83. The cardanic element 83 comprises asphere 88, which is encompassed by the part 89 above the sphere 88 andthe part 93 below the sphere 88. The rotatable element 83, in responseto the placing and pressing process of the device 5 on the substrate 3by the plunge 87, assumes an angle between the normal 95 of the lowerside of the device 5 to be connected and the pressing direction F of thedevice 5, the angle corresponding to the angle between the normal 96 ofthe surface area of the substrate 3 to be connected and the pressingdirection F of the device 5. A possible tilting of the lower side of thedevice 5 in reference to the substrate surface area, which is to beconnected, is individually compensated for by the rotable element 83. Aparallel alignment of the device 5 to the substrate 3 leads to aconstant thickness of the solder layer 13.

The upper and lower ends of the suction line 77 in the sphere 88 mayeach be widened to a funnel having an angle corresponding to the tiltingangle of the lower side of the device 5 in reference to the surface areaof the substrate 3. An example of a funneled lower end of the suctionline 77 in the sphere 88 at the intersection to the part 93 below thesphere 88 is shown in FIG. 10. The lower end of the part 89 above thesphere 88 and the upper end of the part 93 below the sphere 88 may beequipped with suction funnels as well.

It can be seen from FIG. 10 that in the variant of the storing of theplunge 87, an offset develops between the device 5, 6 and the substrate3, 4 during the pressing in response to a compensation of a tilting. Theoffset is minimized when the center of the spherical element 83 lies asclose to the ideal pivot point as possible, which is located in thesurface area of the device 5, 6 to be connected. As illustrated in FIG.10, the center of the sphere 83 may be located at the lower end of theplunge 87.

An offset between the device 5, 6 and the substrate 3, 4 as a result ofa compensation of a possible tilting is prevented by arranging at leasttwo cardanic elements one after the other in the plunge 104 in FIG. 11.The placing point of the lower side of the plunge 107 on the device 5, 6does not change during the pressing process on the substrate 3, 4, dueto the cardanic elements arranged in series. Naturally, more than twocardanic elements may be connected in series. The upper cardanic elementcomprises the sphere 105, the upper part 103, and the lower part 106.The lower cardanic element comprises the sphere 108, the lower part ofthe upper cardanic element 106 being the upper part of the lowercardanic element. The lower cardanic element is locked by the lower part107.

A further example of a cardanic element is illustrated in FIGS. 12, 13,and 14. FIG. 12 shows the assembled cardanic element, which comprisesthe sphere 108, the upper part 106, and the lower part 107. FIG. 13shows an example of the lower part 107, wherein the vacuum suction linesfor receiving the devices 5, 6 are visible. The upper part 106 isillustrated in detail in FIG. 14. The sphere 108 is positioned betweenthe upper and the lower parts 106 and 107 by means of guide screws. Indoing so, the lower part 107 can freely align itself with reference tothe surface area of the substrate 3, 4 which is to be connected.

During diffusion soldering, for example for connecting IGBT or MOSFETdevices (IGBT: insulated gate bipolar transistor, MOSFET: metal oxidesemiconductor field effect transistor) with DCB or AMB substrates,tiltings of between 1 to 20 μm of the substrate surface area, which isto be connected, and of the lower side of the component, which is to beconnected, occur. Particularly the combined use of a rotatable elementfor compensating tiltings and of a spring-mounted plunge, permit acomplete compensation of the tilting between the devices 5, 6 and thesubstrates 3, 4 in response to a homogeneous introduction of a contactpressure F on the devices 5, 6, which are to be connected with thesubstrates 3, 4, so that excessive residual solder can be pressed out ofthe gaps between the devices 5, 6 and the substrates 3, 4 duringdiffusion soldering. An alloying of the entire soft solder with theresult of exclusively intermetallic phases in the solder connectionlayer can thus be reliably achieved.

The apparatus of the novel connection arrangement permits diffusionsoldering of components on substrates by virtue of a highly reducedoxidation of the free surfaces of the components. For this purpose, thediffusion-soldering of semiconductor components on ceramic substrates isaffected in a closed evacuated installation. The result thereof is thepossibility of adjusting a defined oxygen concentration by a gasexchange in the context of the transport of the components and of thesubstrates from a subchamber of the novel chamber into anothersubchamber. Furthermore, other reducing activation media (such as formicacid) may be used in addition to the forming and protective gas. Whilethe forming gas guarantees a sufficient chemical surface area activationonly at temperatures of approximately 400° C., formic acid already hasan activating effect at 170° C.

A combined transfer and pressing unit is located in the closed evacuatedchamber, with which the semiconductor components to be connected arereceived from a storage position and are deposited onto the solderposition, at which the substrate to be connected is located. During thedeposition, a force is exerted on the semiconductor components by thepressing unit, so that the time between the placement and pressing ofthe semiconductor components on the substrates to be connected isminimized.

With solder thicknesses of a few micrometers, such as created duringdiffusion soldering, a tilting or wedge-formation in the solder layer,which is to be applied, may lead to an uncontrolled formation of hollowspaces inside the solder layer and to dents at the solder layer surfaceareas. This leads to a degradation of the solder connection layerbetween component and substrate. During the process of placing andpressing the component on the substrate, an angle appears between thenormal of the lower side of the component, which is to be connected, andthe pressing direction of the component. The angle corresponds to theangle between the normal of the substrate surface area, which is to beconnected, and the pressing direction of the component. This way,tiltings and wedge-formations are avoided in the solder layer to beapplied.

1. An apparatus for connecting a component with a substrate by means of diffusion soldering in a closed evacuated chamber, wherein the component and the substrate to be connected are displaceable separate from one another in the chamber, and the chamber comprises a combined transfer and pressing unit being displaceable between a current position of the component and a current position of the substrate, for placing and pressing the component on the substrate, and the combined transfer and pressing unit comprises a rotatable element, which, in response to the placing and pressing of the component on the substrate, assumes an angle between the normal of a lower side of the component to be connected and a pressing direction of the component, the angle corresponding to an angle between the normal of a surface area of the substrate to be connected and the pressing direction of the component.
 2. The apparatus according to claim 1, wherein a plurality of components, a plurality of substrates and a plurality of rotatable elements are located in the chamber at the same time.
 3. The apparatus according to claim 1, wherein the surface area to be connected of each substrate is covered with formic acid.
 4. The apparatus according to claim 1, wherein the chamber comprises three juxtaposed subchambers.
 5. The apparatus according to claim 4, wherein each of the juxtaposed subchambers comprises process parameters which differ from those of the other subchambers.
 6. The apparatus according to claim 1, wherein the subchambers are connected to one another and with respect to the outside by means of two carrier systems, wherein the substrate is placed on the first carrier system and displaced through the chambers and the component is placed on the second carrier system and displaced through the chambers.
 7. The apparatus according to claim 1, wherein the transfer and pressing unit comprises at least one plunge, wherein each plunge has a vacuum suction element for gripping at least one component.
 8. The apparatus according to claim 7, wherein the at least one plunge is individually mounted in a movable and spring-mounted manner in a direction of the pressing direction of the component.
 9. The apparatus according to claim 8, wherein each plunge is individually connected to a plunge carrier by a spring element, or to the plunge carrier by an elastic cell.
 10. The apparatus according to claim 8, wherein a plurality of plunges are connected to one another by an elastic cell.
 11. The apparatus according to claim 9, wherein the elastic cell comprises an elastomer.
 12. The apparatus according to claim 9, wherein the elastic cell comprises a liquid and a flexible membrane, which seals the liquid.
 13. The apparatus according to claim 7, wherein each plunge comprises an element for compensating a tilting between the substrate and the component.
 14. The apparatus according to claim 7, wherein a plurality of plunges comprise a shared element for compensating a tilting between the substrates and the components.
 15. The apparatus according to claim 13, wherein the element comprises a cardanic element for compensating a tilting between the substrate and the component.
 16. The apparatus according to claim 15, wherein the cardanic element comprises a sphere, an upper part and a lower part, wherein the sphere is arranged between the upper part and the lower part and is mounted with guide screws.
 17. The apparatus according to claim 1, wherein the at least one component is an IGBT or MOSFET.
 18. The apparatus according to claim 1, wherein the at least one substrate is a DCB (direct copper bonding) substrate, an AMB (active metal brazing) substrate, or a regular brazing type substrate.
 19. An apparatus for connecting a component with a substrate, the apparatus comprising: a closed evacuated chamber in which the component and the substrate to be connected are displaceable separate from one another, the closed evacuated chamber comprising: a combined transfer and pressing unit operable to displace between a current position of the component and a current position of the substrate and operable to place and press the component on the substrate, the combined transfer and pressing unit comprising: a rotatable element, which, in response to the placing and pressing of the component on the substrate, is operable to assume an angle between the normal of a lower side of the component to be connected and a pressing direction of the component, the angle corresponding to an angle between the normal of the substrate surface area to be connected and the pressing direction of the component; a first carrier system operable to introduce the component into the closed evacuated chamber; and a second carrier system operable to introduce the substrate into the closed evacuated chamber, the first and second carrier systems being separated from one another.
 20. The apparatus of claim 19, wherein the first and second carrier systems are operable to run parallel to one another inside the closed evacuated chamber between first and second locks operable to seal off the closed evacuated chamber to the outside. 